Organic Light Emitting Diode (OLED) display device, also known as an organic electroluminescence display device, has recently been widely used in mobile communication terminals, personal digital assistants (PDAs), pocket personal computers, etc., due to its outstanding advantages such as self-luminescence, no need of backlight, high contrast, small thickness, wide viewing angle, quick response, suitable for wide temperature range, simple structure and simple fabrication process.
OLED display devices are divided into a passive matrix type and an active matrix type. In the OLED display device of active matrix type, current flowing through each OLED is controlled by a Thin Film Transistor (TFT) circuit, and high luminescence efficiency and good image display effect can be achieved.
As shown in FIG. 1, the OLED display device of active-matrix type comprises an array substrate 110 and a color filter substrate 120. The array substrate 110 comprises: a first substrate 111, and an array of thin film transistors 112, a protective layer 113 and a connection electrode 114 sequentially disposed on the first substrate 111. The connection electrode 114 is connected to a drain electrode of the thin film transistor 112 through a via hole formed in the protective layer 113. The color filter substrate 120 comprises: a second substrate 121, and a color filter layer, a planarization layer 123, a first electrode 124, an organic electroluminescence layer (an organic EL layer) 125 and a second electrode 126 sequentially disposed on the second substrate 121. The color filter layer comprises: black matrixes 1221, and color filters 1222 separated by the black matrixes 1221. After the color filter substrate 120 and the array substrate 110 are bonded with each other, the second electrode 126 on the color filter substrate is in contact with the connection electrode 114 on the array substrate 110 so as to implement an electrical connection between the thin film transistor 112 and the second electrode 126.
In order that the connection electrode 114 and the second electrode 126 are in the stable contact to enhance reliability of the electrical connection between the thin film transistor 112 and the second electrode 126, the connection electrode 114 is generally formed to be relatively thick (typically 2-3 microns thick). Further, if there are impurities adhering on contact surfaces of the connection electrode 114 and/or the second electrode 126, a poor contact may be caused.